Food Digester

Basic Info:
The food digester uses natural organic microorganism, or microbes, to break down food waste in much the same way your stomach does. The digestion turns solid food wastes into a liquid form. The fluid goes straight into the floor drain in the dish room, then into our grease trap. The microbes remain in the fluid as it travels to the grease trap producing far less build up of grease resulting in fewer odors, insects and organisms normally associated with grease build up. Not only does the Food Digester divert food waste from the landfill, it saves in transportation cost and associated energy use.
In Depth Info:
The food digestion process uses aerobic decay, along with a balance of moisture and temperature, to optimize and speed up the digestion. By maintaining optimal environment conditions within this machine, microorganisms that live and reproduce inside the Digester can efficiently work to rapidly break down solid foods. These microorganisms produce different kinds of enzymes that break down different parts of foods. For example, they produce enzymes like protease that help break down proteins. Once these enzymes have rendered food waste into smaller molecules like amino acids, nucleic acids, lipids and carbohydrates, those macromolecules can then be reformed later into new proteins, oils, etc. The resulting mixture is added, along with the microorganism, to the municipal drain water system where water then travels to a waste water treatment plant. The microorganisms added into the water are beneficial to the treatment plant because they help to further release enzymes that break down other biodegradable products that enter the water system in other parts of the community.

Food Pulper

All leftovers including food and napkins get ground up by the food pulper. This food pulp is either added to the Food Digester or taken to our Earth tubs and mixed with Humus, Sawdust and our Bulky Carbon source.



Basic Info:
Food that doesn’t go through the food Digester is added to the Hollins University composting process. Food waste is combined with a balance of wood chips, leaves, and sawdust all of which is put into EarthTubs. EarthTubs speed up decomposition by keeping out rain and wind which can disrupt the composting process. After the compost maintains a certain temperature consistently for a few days, the bad pathogens in the compost have been killed because they can’t survive in the heat .All the good aspects of the compost which make up healthy soil remain in the compost. Once the compost reaches this stage, we move it into what we call a windrow, stage two of the process.

In Depth:

Approximately half of all the food waste generated through dining services is used in on-site composting. The word compost comes from two Latin words: com meaning “to bring” and post meaning “together”. When we bring together nitrogen, protein, carbon, moisture, and air, compost happens. Composting, then, is a controlled effort to manage what occurs naturally during the rotting process of all living matter. Civilizations have been composting for thousands of years. The composting process occurs through the work of billions of microorganism (mostly bacteria) breaking down proteins. Carbon is the energy source for the microbes. They work best with adequate moisture and plenty of oxygen, just like a fire. The bi-product of their activity is heat. As the temperature increases during the process, different types of microbes come into play. These microbes can be classified into three major groups: psychrophiles, that work at lower temperatures, while mesophiles work in warm temperatures, and thermophiles in hot temperatures. All three groups of microorganisms can, and often are, working in the compost pile simultaneously.

The result of these microorganisms efforts in the compost pile is humus. The final product does not in any way resemble the initial components. Humus is rich in organic matter full of helpful microorganisms, it holds moisture and soil nutrients well, and is very beneficial to plant growth and overall health. Humus allows us to replenish the earth with much of what we reap while growing plants.

Hollins uses two EarthTubs to compost food waste. Food waste is our source of nitrogen. We add sawdust, leaves, and compostable paper products as a carbon source. Leaves are very plentiful on our campus, and our Theater Scene Shop produces sawdust. Also, our dining services purchased compostable food service paper products for most of the catered events across campus. Moisture is controlled by lids on the EarthTubs and oxygen is encouraged by use of an auger that rotates around the EarthTub stirring its contents. It generally takes about six weeks to produce quality humus using our EarthTubs.


The idea of a windrow is to take healthy compost that has reached a minimum of 140 degrees from our Earthtubs, taking about a week, then putting the material into an environment that still allows the compost to thrive while also helping to decompose other carbon products like leaves. A windrow consists of a row of leaves holding actively composting material in the middle and then covered with more leaves. This keeps the compost insulated and hot enough to keep composting at a fast rate but also allows more air to draw into the compost and help feed it like a fire. Because of this set up, the leaves around the compost will begin to rapidly decompose and produce humus. By adding the humus produced by the EarthTubs into a larger carbon source, we are able to generate a large quantity of humus by having the EarthTub material rapidly breakdown the leaves added to the windrow. After sifting the humus for large particles such as wood chips, the humus is ready for use.